Field of the Disclosure
The present disclosure relates to an organic light-emitting diode display device, and more particularly, to an organic light-emitting diode display device capable of improving a lifetime.
Discussion of the Related Art
Recently, flat panel displays have been widely developed and applied to various fields because of their thin profile, light weight, and low power consumption.
Among the flat panel displays, organic light-emitting diode (OLED) display devices, which can be referred to as organic electroluminescent display devices, emit light during loss of electron-hole pairs. The electron-hole pairs are formed by injecting charges into a light-emitting layer between a cathode for injecting electrons and an anode for injecting holes.
The OLED display devices can be formed on a flexible substrate such as plastic. Since they are self-luminous, the OLED display devices have excellent contrast ratios. The OLED display devices have a response time of several micro seconds, and there are advantages in displaying moving images. In addition, the OLED display devices have wide viewing angles as they are self-luminous.
OLED display devices are divided into passive matrix type OLED display devices and active matrix type OLED display devices according to a driving method. Active matrix type display devices having a low power consumption and a high definition are widely used. In addition, the size of active matrix type display devices can be large.
An OLED display device includes a plurality of pixels to express various colors. Each pixel includes red, green and blue sub-pixels, and red, green and blue organic light-emitting diodes are formed in the red, green and blue sub-pixels, respectively.
The red, green and blue organic light-emitting diodes include red, green and blue light-emitting material layers, respectively, and each light-emitting material layer is formed by a thermal evaporation method. More particularly, the light-emitting material layer is formed by selectively vacuum evaporating an organic light-emitting material using a fine metal mask. However, the thermal evaporation method is difficult to apply to display devices having a large size and high definition due to manufacturing deviations, sagging and a shadow effect of the metal mask.
To solve this problem, a method of forming the light-emitting material layer through a solution process has been suggested. In the solution process, a bank layer surrounding a pixel region is formed, a light-emitting material is dropped in the pixel region surrounded by the bank layer by scanning a nozzle of injection apparatus in a certain direction, and the dropped light-emitting material is hardened to form the light-emitting material layer. At this time, a hole injecting layer and a hole transporting layer also may be formed through the solution process.
By the way, the red, green and blue light-emitting materials each have different characteristics. Specially, the red light-emitting material has relative low efficiency and the green light-emitting material has relatively short lifetime. Thus, it is not easy to secure red, green and blue light-emitting materials having uniform lifetime and efficiency, and a lifetime of the OLED display device is reduced.
Meanwhile, reflection of the external light is high in the OLED display device. The reflection of the external light increases the brightness at black state, which reduces the contrast ratio and degrades image qualities. Thus, in order to prevent the reflection of the external light, at least one polarizer is used, and this causes an increase in costs.